Effect of magnetic field on melt flow and crystal growth of oxide crystals

Progress in Crystal Growth and Characterization of Materials (1999)261-272

PERGAMON EFFECT

Progress in Crystal Growth and Characterization of Materials

OF

MAGNETIC

FIELD OF

ON

MELT

OXIDE

I-i

Institute Namiki,

for

AND

CRYSTAL

GROWTH

CRYSTALS

Yasuto

National

FLOW

Miyazawa

Research

Tsukuba-shi,

in

Inorganic

Ibaraki

Materials

305-0044,

Japan

ABSTRACT

The

flow

in

magnetic

an

Czochralski flows

oxide

field

in

was

equipment

oxides

semiconductor magnetic

melt

for

melts melt.

field

by

such

observed

were

The

as

by oxide

this

and

T i O 2 in

a

high

magnetic-field-applied

crystals.

very

single

using

LiNbOj

using

much

It

was

different

crystals

of

found

from

TiO~

that

these

the

in

were

grown

in

melt;

flow

in

field

to

a a

equipment.

KEYWORDS

Magnetic melt;

field

flow

applied

pattern;

Czochralski;

spoke

MCZ;

oxide

pattern

INTRODUCTION

It

is

well

known

semiconductor flow

in

single

the

that

melt melt.

crystals

field-applied

by

when

the

kinds

a magnetic

This the

as

of

application Si,

effect

Ge, has

been

(MCZ) [1,2]

field

that

(especially

a magnetic or

are a

InP

widely

method

Czochralski(MLEC) effects

of

GaAs

Czochralski

Czochralski

liquid-encapsulated about

the

such

or

used

namely

by

to

a

the

grow

magnetic-

magnetic-f~eld-appl]ed-

. However, produced strong

Jn

little an

magnetic

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attenuates

oxide

is

known melt

field)

is

EMiyazawa/Prog, C~smlGrowthand~aracL38~999) 2 6 1 ~

262

applied.

In

usually

an

several

semiconductor

In

no

this

field

melt,

orders melt.

attenuation know,

oxide

of

effect

is

chapter, on

it

may

negligible work

we

oxide

electrical

magnitude

Hence,

experimental

has

the

had

document

smaller be

in

than

expected an

been

the

conductivity

oxide

effect

that

that

that

of

the

melt.

reported

is

AS

a

flowfar

in

this

an

applied

as

we

area. magnetic

melts.

FLOW

EXPERIMENTS

Equipment

Since, the

no

new

apply

a

effect

oxide

MCZ

apparatus

equipment. strong in

An

MCZ

magnetic

oxide

melts

existed,

pulling

field was

to

an

it

specifications

for

the

type

specific

(vertical,

the

field

strength.

determined

by

Vertical

field

Transverse Cusp

The (i)

field The

cost

and

final

field

above It

field was

this

to

melt.

was

design

- 0, 8 T

0

- 0.16

flow

of

or the

for

cusp)

and

magnet,

are

as

as

follows:

T

were

choose

the

determine

particularly

considerations,

- 2.0

to

make

to

Because

transverse

0

and

modified

difficult

apparatus,

0

specifications

possible

to

was

specifications

technical

field

had

oxide

unknown,

appropriate of

we

apparatus

T

unique

from

because:

three

types

of

magnetic

field. (2)

The

maximum

apparatus the

field

used

for

vertical

strength

were

much

semiconductors

field(which

is

higher

than

especially

for

usually

0.i

to

that the

several

of

the

case tenth

of of

Tesla). (3)

It

was

possible

to

reverse

the

polarity

of

the

applied

field.

In

semiconductor

at

about

0.1T.

applying

the

generated of

this

by magnet

(vert J c a l

and

melts, The

same

the

attenuation

effect

may

maximum

vertical

using

superconducting

a

system

is

transverse)

shown were

be

field.

in

effect

expected These

generated

A

The by

oxide

magnetic

magnet. Fig.l.

usually in

appears melts

fields

conceptual two

types

switching

by

were figure

of

field

E Miyazawa /Prog. Crystal Growth and Charact. 38 (1999) 261-272

two

pairs

coils. cusp

of

And

263

field

the

field

were

C. I

generated

by

changing

the

connection

of C~nn~¢tor

field

coils

vertical Fig.2,

for

field.

In

connections shown.

It

possible

were was

to

the

polarity

the

field

switching polarity

also

change of

0

by

o

the

o ,-4

of

current

source

already

mentioned.

The

furnace

pulling of

and

apparatus

similar

those

as

component

the

were

---,¢

those

in

to

the

usual Fig.l

Czochralski apparatus

for

oxide

construct

the

equipment

aluminum)

because

Beside

the

because

the

could

(maximum

output)

a

very

rare

semiconductor

Flow

The

be

all

magnetic

of

used.

To

that

MCZ,

to

only

the

furnace

was

heat

crucible,

RF

resistive

50

to

60 a

60

for

heating

to

steel

diameter

kHz, was

50

kw

used.

MCZ,

since

in

method

had

been

It

used.

Experiments

experiments

both

transverse

popular field

oxides, was

designed and such

gradually

to

vertical as

observe

LiNbO~,

increased

the

magnetic GGG, from

flow

fields TiO~,

0 to

in

etc.

its

oxide

used The

maximum

or

large. small

mm

RF-generator

heating

used

quite

relatively

only

use

materials

was

magnets, the

system

(stainless

leakage

transistor-inverter case

of the MCZ

nonmagnetic

field

the

the

portion

except

were

holding

size

crucible

was

the

chamber

of

crystals

Magnet

melts

in

several magnetic and

it

was

2~

ZMiyazawa/Pmg. C~smlGmw~and~aract. 38d99~261-2~

held was

period

decreased

for In

for

an

to

melt,

removed set

at

to

the

the

observe

the

CCD

of

used

the In

only

used.

for

flow

to

it

use

the

super-conducting

cover

the

chamber.

was

melt

fed

into

and

recorded.

The

LiNbOj

could

were

The

by

the

observe

the

chamber

at

spoke kept

from

zero

held

at

video were

be

. . . . . . . . . . . .

Fig.2 Field coil c o n n e c t i o n (1)Vertical

observed

field

(2)Cusp field

The

and

in

mm

was

pattern of

usual

The

air,

and of

to

its

maximum

value

for

10

The

performed

for

the

both

entire

the

temperature

50

height

mm

the

in

As

flowed

that

the

melted,

several

and

and to

the

visualize it w a s

hours

to

applied-ramping

period was

a mm

atmosphere

were

a time

1.5

unable

through

reduced

of

12

recorded

experiment.

vertical

was

powders

pattern

24

apparatus it

then

4000

into

and

to

was

of for

possible

for

its

and

loaded

pulling

melt.

field

over

flow

pressure

made

temperature

zero

during

so

the

of

LiCO~

was

N~ g a s

the

magnetic

min.

that

the

it

4N-pure

at

field

because

material

in

form

cm~/min

all

seeding

melt.

at the

placed

flow

. After

held

to in

2000

pressed

Then

first

mixed

diameter,

generator

Marangoni

recorder

performed

congruently

50

a rare

the

were

H~O.

spoke

the

~

monitor

crucible

pattern[4] at

magnet

i100°C,

RF

the

stabilized

i

tracers

CO 2 and

crucible

emphasize

i

isostatically

to

remove

thickness. heated

,j>

No

experiments

k g / c m ', h e a t e d

platinum

,

image

a TV

point.

Nb~O~ p o w d e r s

to

~

(3)Transverse

melt

melting

hours

i

order

recorder so t h a t t h e flow pattern on the

surface

lower

The

i

~

was

any

since

~

at

spoke

was

because

(2)

flow

melt.

very

and video m o t i o n of

~

in

was

visualization,

signal

(I)

G flow

was

flow,

difficult

i

held

axis

the

the

pattern

were

it

camera

center

the

flow

tracers

and

pulling

of

then

period.

observe

surface

like

zero

the top

to

time,

observe

and

chamber the

to

additional

order

the

of

Similar

transverse

min, by

and

the

experiments magnetic

field. Next

TiO~

powders

melt

were

experiments pressed

at

the

were

performed.

pressure

of

The

4000

pure

TiO~

kg/cm ~ by

4N

CLIP,

then

YMiyazawa/P~g.C~smlG~w~and~arac~38H99~261~ it

was

The

sintered

prepared

crucible

furnace.

charged

was

50

was

stabilized,

for

the

The

In

by

the

same

period.

the

case of

regular

the

the

of

the

Tesla

was

there

very

magnetic

suddenly

RF

2000

at

almost

the

was

height

hours.

by

k g / c m ~ in and

the

1.5

mm

the

temperature

bottom

center

After

the

temperature

was

of

then

24

the

field

strength

for

iridium

mm

heating

magnetic

minutes,

started

was

slow

As

applied

2.0

T

lowered

same

in

to

of

to

the

about

the

0

experiments

20

field

but

with

performed.

increase

monotonically

the

bottom

was

evident

the

Up

with of

to

was

the

about rate

magnetic

crucible

started

difference

the

of

the

flow at

a

seemed

The

to

temperature

increase zero

when

direction

center

field. to

a

flow

rotation

from

several

However,

flow

further,

the

60°C

The

stable.

T,

increased

The

below change;

observed.

0.8

gradually rpm.

field

flow-pattern was

flow

field

several

center

began.

a vertical

about

rotate

rate

in

pattern

and

the

rotation

rotation

no

reached

to of

melt

spoke

field

changed.

pattern

when

magnetic

flow field

observed.

This

phenomenon

was In

semiconductors.

attenuated

above

viscosity

is

the

causes

flow

no

field.

When to

the

flow

pattern

of

This

the

2.0

field

observed

in

flow

velocity

is

the as

was

reverse

After

shown

to in

the the

0. i T) . T h e

magnetic our

observed.

hysteresis

melt.

is

flow

far

were

field

the

changed T

the the

(about

applying As

from melt,

monotonically

magnetic

pattern at

by

effects

almost

hysteresis.

viscosity

critical

increased

zero,

different

semiconductor

attenuation.

such

velocity

value

a

very

a

increased

flow

concerned,

the

pure

50

of

measured

field

LiNbO~

symmetrical

velocity

some

rate

field

Next,

of

3N

by

thermocouple.

maximum 10

1500°C

Results

tenth

at

a

about

direction

a by

was

vertical

the for

at

at

the

diameter

melted

which

attaching

0 to kept

reverse

was

into

mm

flowed

1850°C

crucible

minutes,

was

sample

about

from

temperature

was

the

melt

furnace

size

N~ g a s The

at

a

sample

whose

thickness.

held

in

265

In

decreased

Fig.3.

In

LiNbO,

from

the

the

to

case

maximum

of

by

about

pattern.

the

magnetic

observed

caused

reached spoke

were melt,

applied

was

probably

normal

a

the

phenomenon

field

which

experiments

with

was

effective

field,

with the

high

0.5

T,

The

flow

transverse

2~

YMiy~awa/Prog. C ~ s t a l G ~ w ~ a n d ~ a m c t 3 8 ~ 9 9 ~ 2 6 1 ~

field, to

similar

change

pattern the

at

than

flow

and

field.

By

almost

T

is

in

flow

the

the

the

as

in

in

the

2.0T)

effects

were

of

vertical but

In

magnetic

the

and

the

simple

current of

but

flow

pattern

symmetrically

was

observed case.

value

(0.8

with

some

The

pattern

Fig.4 The flow p a t t e r n

T)

to

at

when

applied, was

much

melt,

was

that

into

the

the as

not

a

changed

Fig.5 The flow p a t t e r n (vertical

in TiO2

0.1T)

center

flow

the

changed about

in LiNbO3

0.8T)

in

convection

and

soon

maximum

magnetic

rather

network

crucible,

L i N b O 3. As

its

field

applied

applied

the

melt,

LiNbO~

pattern

flowed

vertical

the

fields,

was

in

The

from

with

essentially the

differences

spoke

time.

to

observed

TiO~

pattern,

complicated with

but

(transverse

convection

than

field;

increased

started

complicated

normal

field

in b o t h

field

natural

stronger

pattern

vertical

phenomenon

transverse

the

flow

a more

a direction

in LiNbO3

fundamental

some

existed. no

TiO~,

and

to

Fig.4.

(vertical

case

of

to

the

The

changed

velocity

Fig.3 The flow p a t t e r n

Similar

observed.

It case

reverse

just

shown

T.

changed

decreasing

hysteresis, 0.8

that

the

were

0.5

direction

field,

zero,

results about

velocity

was

vertical

magnetic

drastically.

It

center,

as

shown

higher

started in

than

field

was to

Fig.5.

that

in

applied,

rotate (just

as

the

this

EM~azawa/P~g.C~smlG~w~and~amc~38~99~261~ LiNbO 3 melt rate

had

however,

critical

in

a very

was

field

strength

although

the

0.01

T,

This

rotation

magnetic

of

field. linearly

not

LiNbO~ melt.

The

the

same

case

as

the

changed

flow

with

the

transverse

of

the

field

strength

could

was

not

expected

rotation

applied of

but

never

under

similar in

such

to

the

applied,

started

to

than

measured. low

the

case

TiO 2 melt

symmetrical

was

less

be

monotonically,

field

the

L i N b O 3. T h e was

not

increased

LiNbO 3 with

rotation

in

begin

rotation

field

The

that

to

magnetic

crucible

than

rotation

of

the

field).

higher

this

direction

drastically,

toward

for

rate

the

magnetic

times

exact

the The

but

When

high

several

267

of was

flow.

the

rotate.

flow

It

pattern

flowed

wall.

Discussion

It

is

very

results

difficult

because

semiconductor oxides

melts.

melts

are are

negative

ions

are

then

the

Lorentz

ions

instead

may

The

be

It

mobility

possible

is

of

to

as

that

act

is

they on

electrons, these

and

this

and

may

two

are

it

ions

no

flow

charge

in

heterogeneous

charge and

not

dose

positive

evenly

in

distributed,

and the

negative

semiconductor

different,

effects

in the

both

positive

are

experimental

from

the

melt

both

as

these

these

different

a whole If

explain

GROWTH

explain

believed

separated

free

to

extremely

present.

force

of

present

are

neutral

distributions

melt.

at

they

by

therefore

computer

it

simulation.

EXPERIMENTS

Introduction

It

is

very

difficult

Czochralski very

unstable,

drastically. The

so It

rutile(TiO2)

materials. grown

Large

either

present.

to

technique,

But

it

cannot

grow

is

very be

crystals and

TiO~

because

good

single

the easy

to

obtained have

flame

fusion

by

using

these

for

crystals

methods,

or

the

than

used

method

of

change

more

been

quality

by

crystals

diameter

I0

are

thermal

the

crystal

is

diameter mm

length[3]

optical

floating

the

by

the

needed. zone

.

isolation It method

distortion

is at is

ZMiyazawa/Prog, C~stalGrow~and~aract38~99~261~

268

quite By

big,

now,

been

therefore

the

for

applying After

flow It

interface. the

be

is

rotates

Growth

TiO~

the

clockwise

in

melt

was

the

may

be

the

effect of

the

difficult

to

so

that

the

melt

possible

melt,

method.

which

to

keep

controlling

Czochralski

to

was

keep

providing

But

produces

the

that

the

seed

the

flow

direction.

the

The

same

growth

way

as

described

conditions

of

in

these

experiments

were

following.

Pulling

rate

Magnetic

The

crucible

was

set

to

and

the

caused

The

melting

and

the

regular

melt

direction

the

has

spoke

the

of

by

makes If

flow will of

be the

TiO~

strong but

seed

rate

applied

crystal

was

was

is

counter

of

the

flow

magnetic

set

to

field

10-30

direction

relatively

convention

difficult

will

somewhat

rotation the

a networked

vertical

pattern

the

liter/min)

to

rpm the

field.

of

it v e r y the

of

(2

(0.02-0.04T)

the

rotation

magnetic

very

but

adjusting

rate the

pattern,

rpm N~ g a s

vertical

rotated, rpm

temperature

crystal.

flow

i0

mm/hr

10-30

:

rotation

by

convection

melt,

not

direction

one

:

pure

field

was

The

2-4 rate

:

about

strength.

:

rotation

Atmosphere

the

it

toward

prepared

part.

Seed

the

by field

drastically.

this

shape

melt

MCZ

by

Experiment

experiment the

the

has

were

the

melts,

of

the

method

with

changes

very

crystals.

EFG

crystals

oxide

melt

it w a s

toward

flow,

concave

many

in

impossible

or

the

utilization

magnetic

shape

of

controlling

concave

almost

in

TiO~

quality

experimenting

flow

for

high

Czochralski

quality

the

for

a vertical

obtain

been

that

the

used

counterclockwise

interface

the

found

example, shape

diameter

the

and

to for

have

field,

may

For

applying

We

observation,

interface

the

size

yet.

magnetic

proposed.

by

and

the

oxide,

the

hard

but

satisfactory

method

is

trial

tried,

not

it

experimental

magnetic change

very

crystal

to

to

stable. is

high

flow, flow

which

field

If

opposite

the

is

the

not

This

diameter

applied

vortex

to

is

pattern.

control

the

(about

like

to flow

rotational the

current

1850°C) a strong of the and

Y M~awa/P~g.C~stalG~wthand ~amct. 38(199~261-2~ produced

by

the

crystal

the

control

the

single

window

of

the

magnet crystal

was

weight

of

The

the

growth

is

crystal

which and

the

shown example grown in

The

time

The

If

impossible

to

the

the

crystal

this

cell

was

was

whether

Therefore

by

the

low

answer,

and

the

it

-

-

it

2

was

of

the Fig.6

The p h o t o g r a p h of g r o w i n g crystal

as

magnetic it

grow

was

that

Czochralski

very the

technique

-

effective

for

load

in

of may

Fig.7 The e x a m p l e of as

grown crystal

was

cell

the be

growing the

automatic

possible

to

such

constant

crystals temperature

as

T i O 2. If bath

diameter

control

system

grow

crystal

of

the

flow

pattern

in

many

oxides

melt

change

longer

drastically

and

is

CONCLUSION

The

by

monitoring

not

too

--

shown

field

put

applied,

load

application

magnetic

can

no

the

certainly we

again,

the

judge

was

present,

of

But

to

smaller.

view

because

interface

field

method,

the

or

crucible

The

expected.

by

difficult

bigger grow

the

grow the

in

was

which

length

to

to

to

but

the

maintained

was

very

tried

crystals,

of

makes

was

about

mm

photograph

convex

we

seed

shape

which

photograph

crystal

was

fact,

In

position

was

tried

and

Fig.6.

Fig.7.

shape

melt,

using

getting

of

interface

the

big.

grow

was

20

growth in

we

too

to

cm

of

It

was

crystal.

anyway,

diameter.

big.

the

easier.

a vertical

experiment

possible long

very

field, toward

coefficient

cell

performed was

in

the

convex

TiO 2 by

sensitivity

temperature of

of

cell,

the

magnetic to

diameter

diameter

a load

because

the

almost

the

the

applied change

crystals

was

using

the may

269

by

size.

YMiyazawa/P~g.C~stalG~wthand~amc~38~99~261~

270

applying

a magnetic

differs flow

by

oxide

experiments

melts.

It

glass

was

very

one

in

melt.

that

formers,

little,

glass

In

general, spoke

if

reversed,

It

as

reason

effect.

The

that

it

the

uses

be

magnetic

is

from if

was

the

be

top

the

to

in

And

the

the

may

cause

is

why

this

discussion

non-uniform

melt.

bottom,

direction

reason

mentioned to

of

and

some

Lorentz

the

experiments

by

heating,

Then

it

produce

that

etc.)

and

the

cause

is

this

utilization

the

of

is

may

some

of

is

force

current using

and

in

MCZ

found

the

thermoelectric

conductivity,

than It,

field

mixing

may

rod

a

although

a

some

to

hold

different

current

in

the

to

solve

effect

to

considered:

the

metal.

conductor motive

melt.

may

melt,

the

electric

required

be

several

semiconductor

used

melt

to

obtain

uniform

or

it

be

useful

(2)Control the

may for

of

and

may

be

the

diameter

the

possible of

of

applied to

impurity

Bridgeman

TiO~,

Further

this

growth

problem.

of

the

to

convection

rotation, distribution

remove

in

it

in

bubble

the

may

melt,

be

the

formation.

This

technique.

shape if

we

choose

vertical

control

crystal.

the

crucible

possible

interface

case

enhance

or

crystal,

crystal

flow

The

resistive

some

(Pt,

possible

in

flow.

effect

using

As

As

considered

has

application

Applied

be

rotating

vortex

And

heating

kind

simulation

without

may

in

RF

same

crucible

following

(1)Mixing

have

field

melt.

smaller

may

and

yet.

the

may

formed.

and

the

melt

between

experiments

for

that

heating.

crucible

is

crystal,

tried glass

former

field

seemed

exist

which

RF

magnitudes

Therefore,

As

have

magnetic

showed

large

clockwise.

clear

the

oxide

a metal

force,

of

vertical

melt

in

apparatus

junction

network

that

tried

Another

and

melt

may

ions

We

of

these

effect

several

melts

high

glass

this we

in

glass in

counter-clockwise.

not

thought

effect

order

popular change

no

rotates

oxide

each

be

pulling

case,

of

applied

current

melt.

same

is

the

for

most flow

of

field

had

rotates

occurs

may

the

the

it

electrical acts

extreme

magnetic

a pattern

pattern

section,

the

degree

.

the

effect

in

the

none

that

(27Bi~O356PbO17Ga~O3), observed[5]

In

the

and

melt

however,

a vertical

found

network

were In

each

field,

the

the

magnetic interface

rotation field shape

rate

of

adequately, and

to

control

it

EMiyazawa/Pmg, C~stalGrowthand~amcL38~99~261-2~

271

REFRENCES

[l]A.F.Witt,

C.J.Herman

and

H.G.Gatos,

J . M a t e r . Sci.

5,822(1970). [2]K.Hoshi, Extended

T.Suzuki,

Abstracts,

Y.Okano May

[3]H.Machida

and

[4]S.Morita,

H.Sekiwa,

Soc. [5]H. Of

Of

Japan

N.Isawa,

ECS

Meeting,

T.Fukuda,

J.Cryst. Growth

H.Toshima

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112,

835(1991)

Y.Miyazawa,

J.Ceram.

10111],108(1993)

Minamikawa, Japan

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K.

Takahashi

106111],106(1998)

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Y Miyazawa / Prog. Crystal Growth and Charact. 38 (1999) 261-272

bibliography Yasuto Miyazawa was born in Nagano Prefecture, Japan. He was graduated from Tokyo Institute of Technology in 1963. After working on the TIT, for several years, he moved to Stanford University. He received Phd degree in the department of Materials Science in Stanford University in 1973. He joined National Institute for Research in Inorganic Materials in 1974. Since then, he had been working on the growth of single crystals of oxide materials by the Czochralski method more than 20 years. At present, ,he is mainly working on the flow behavior in oxide melt in strong magnetic field..